1. Field of the Invention
This invention generally relates to an ophthalmic composition comprising an antimicrobial preservative having a cationic group and more particularly, to an ophthalmic composition comprising an antimicrobial preservative having a cationic group which inhibits the antimicrobial preservative from adsorbing to contact lenses while remaining fully antimicrobial.
2. Prior Art
Various antimicrobial preservatives are used in eye drops or ophthalmic solutions. For example, compounds having a cationic group such as benzalkonium chloride, benzethonium chloride, and chlorohexidine gluconate, chlorobutanol, p-aminobenzoates, and sorbic acid are used alone or in admixture of two or more.
Among these antimicrobial preservatives, compounds having a cationic group are widely used in eye drops due to their excellent antimicrobial activity. Undesirably, these antimicrobial preservatives have good affinity to contact lenses, especially soft contact lenses. If an ophthalmic solution containing such an antimicrobial preservative is instilled to an eye with a contact lens put on, the antimicrobial preservative adsorbs to the contact lens. With repeated instillations, the antimicrobial preservative accumulates in the contact lens. The adsorption and accumulation of the antimicrobial preservative can cause chemical and physical degradation of contact lenses. The use of contact lenses having the antimicrobial preservative accumulated therein can cause eye damages.
There is a demand for an ophthalmic solution which can be instilled to eyes without wearing contact lenses, especially soft contact lenses off and which has improved shelf stability. In order to develop such an ophthalmic solution, means for inhibiting the cationic group-bearing antimicrobial preservative from adsorbing to contact lenses is necessary. Various proposals have been made as the anti-adsorption means. For example, Japanese Patent Publication (JP-B) No. 15008/1980 discloses to add a nonionic surfactant to an ophthalmic solution comprising a cationic group-bearing antimicrobial preservative. The nonionic surfactant, however, is not fully effective for inhibiting the antimicrobial preservative from adsorbing to contact lenses. The remaining proposals are also not so successful in providing effective anti-adsorption means.
An object of the present invention is to provide an ophthalmic composition comprising an antimicrobial preservative having a cationic group which not only remains fully antimicrobial, but also inhibits the antimicrobial preservative from adsorbing to contact lenses so that the composition can be instilled to eyes with contact lenses on.